EP0142552B1

EP0142552B1 - Insulation of vessels having curved surfaces

Info

Publication number: EP0142552B1
Application number: EP84902146A
Authority: EP
Inventors: Hiroshi Tonokawa; Hubert Stacy Smith; Emil Ekker
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1983-05-09
Filing date: 1984-05-04
Publication date: 1987-07-29
Also published as: FI850076L; BR8406894A; EP0142552A4; JPS60500821A; AU558074B2; DE3465060D1; IT8420858A1; EP0142552A1; PL247579A1; WO1984004514A1; ES532287A0; KR840008835A; CA1225605A; IT8420858A0; FI81545B; PL146941B1; AU2962484A; ES8505011A1; KR910001696B1; FI850076A0

Abstract

A vessel (10) with a curved surface (13) is insulated with the first layer of insulation (14) formed of a plurality of closed loops (15) joined to each other. A second layer of insulating material (17) is disposed over the first layer (14) and is comprised of a plurality of closed loops (18) of insulating material with adjacent portions of the loops (18) being affixed to each other. Such arrangement allows thicker insulation without the requirement of increased space and heavier equipment.

Description

The invention relates to an improved insulated cryogenic vessel comprising at least a first containment vessel having an exterior curved surface, a first layer of a foam insulation disposed adjacent the exterior surface and covering at least a substantial portion thereof; the insulation being in the form of a plurality of turns of a composite strip-like material, having a continuous gas barrier layer affixed thereto remote from said containment vessel, adjacent turns of the first insulation being heat bonded to adjacent turns of the first insulation.
An insulated cryogenic vessel of this type is known from US-A-4.050.607. That vessel is insulated by means of a spiral generation process, thereby providing a single layer of insulation, having a continuous gas barrier layer affixed thereto. Under normal conditions an adequate insulation and protection ofthe cryogenic vessel is provided. As the value of liquefied natural gas increased relative to heavy fuel oils it became desirable to have increased thermal insulation on vessels employed to transport and/or store liquefied natural gas.
According to the invention such increased thermal insulation is achieved by a second layer of foam insulation being disposed over and unadhered to the first layer of foam insulation and external thereto and spaced from the continuous gas barrier layer affixed to said first layer of insulation; the second layer of insulation being in the form of a plurality of turns of strip-like material, adjacent turns of the second layer of insulation being heat bonded to adjacent turns of insulation of the second layer of insulation; the first layer of foam insulation being a laminated strip-like material, the first layer of foam insulation having affixed thereto a first reinforcing scrim and which in turn has affixed thereto said gas barrier layer, with a second reinforcing scrim located within the laminated strip-like material, the laminated strip-like material defining a plurality of longitudinally extending slots opening toward the exterior surface of the containment vessel, the slots terminating at a location generally adjacent said second reinforcing scrim.
The outer insulating layer provides additional thermal insulation and mechanical protection for the vapour barrier layer which is further protected by a reinforcing scrim, affixed thereto, to provide increased mechanical reinforcement to resist thermal stresses. The first layer of foam insulation is further improved by a second reinforcing scrim as an effective means of terminating any cracks which might result from shrinkagewhile a plurality of slots are present in orderto provide stress relief. In orderto increase the degree of reliability from a containment point of view preferably a second vapour barrier is affixed to the second insulation layer remote from said gas barrier layer. In the event of any leakage of the liquefied gas from the tank this second vapour barrier keeps the system insulated from its surroundings.
If more extreme conditions are experienced a second set of longitudinally extending slots may be applied, such slots extending from said second reinforcing scrim towards said gas barrier layer.
Further features and advantages of the present invention will become more apparent from the following specification taken in connection with the drawing wherein

Figure 1 is a fractional view of a vessel being insulated in accordance with the present invention;
Figures 2, 3 and 4 depict cross sectional configurations of insulation applied in accordance with the present invention.

In Figure 1, there is schematically depicted a fractional view of a vessel 10 being insulated in accordance with the present invention. The vessel 10 has a generally spherical configuration having an external surface 13. Adjacent the external surface 13 of the vessel 11 is a first layer of insulation 14 which is formed of a plurality of closed loops 15 of insulating material which are joined to each other. A second layer of insulating material 17 is disposed external to the layer 14 of insulating material. The layer 17 comprises a plurality of closed loops 18 of insulating material, the adjacent portions of the loops 18 being affixed to each other. A spiral generation depositing apparatus 20 is rotatably mounted adjacent the tank 11 and spaced therefrom. The spiral generation apparatus 20 comprises an arcuate boom 21 having an upper or axial end 22 and a lower or equatorial end 23. The ends 22 and 23 are supported by means of rollers 24 and 25 respec- tiveiy. The upper end 22 of the boom 21 is rotatably fixed to an axially disposed pivot 27 affixed to a dome 12 of the tank 11. An insulation depositing head 28 is supported by the boom 21 and is adapted to move along the boom 21 between the ends 22 and 23. A strip or log of insulating material 31 is engaged by the depositing heat 28 and is effectively wound around the vessel 11 to form the second insulating layer 17. Both of the insulating layers 14 and 17 are deposited by the depositing apparatus 20 which rotates about the vessel 11 as the insulation is deposited.
In Figure 2 there is schematically depicted a cross sectional view of a portion of insulation 40 in accordance with the present invention. The insulation 40 has a first or inner side 41 and a second or external side 42. The insulation 40 comprises a first or inner layer 43 and a second or outer layer 44. The inner layer 43 comprises a plurality of loops or turns of a synthetic resinous thermoplastic foam insulating material 45 each of which comprises a first or inner log portion 46 and a second or outer log portion 47. Adjacent portions of the turns 45 are joined together at joints 48. Advantageously, such joints 48 are formed between adjacent turns by heating the thermoplastic foam of log portions 46 and 47 to a temperature sufficiently high so that, in effect, the foam melts and the adjacent turns are heat bonded together. The inner surface 41 of the insulation 40 has disposed thereon and affixed thereto a reinforcing scrim 49. Advantageously, the reinforcing scrim 49 is an open weave glass cloth which provides mechanical reinforcement for the log portions 46. Each of the turns 45 defines slots 51 which extend from the inner face 41 partially inwardly and in a direction generally normal to the log portions 46. A reinforcing scrim 53 is disposed between log portions 46 and 47 and heat bonded therebetween. The scrim 53 advantageously is an open weave glass cloth and provides mechanical reinforcement for the turns 45. The log portions 47 remote from the inner face 41 have affixed thereon an optional glass reinforcing scrim 54, which, in turn, is adhered to a vapor or gas barrier layer 55, advantageously of aluminum. The vapor barrier layer 55 is wider than the turns 45 and is heat sealed by means of appropriate hot melt adhesives to adjacent portions of vapor barrier material 55 on adjacent turns 45. Each of the turns 45 adjacent its edges defines a recess 57 adjacent the inner or cold side 41 and recesses 58 adjacent the vapor barrier layer 55. Advantageously, the adjacent recesses 57 form a groove on the inner face 41 to provide clearance for a heat sealing platen when the joints or fused portions 48 are formed. The grooves 58 facilitate the sealing of adjacent portions of the vapor barrier layer 55 and folding of the sealed portions so that the sealed portions lie generally parallel to the major portions of the vapor barrier layer 55. The outer insulation layer 44 comprises a plurality of loops or turns 61. Each of the turns 61 has a body portion 62 of a synthetic resinous thermoplastic foam insulating material and an inner face 63, having affixed thereto an optional reinforcing scrim 64 such as an open weave glass cloth. The body portion 62 has an external or outer face 65 having adhered thereto a reinforcing scrim 66 which in turn has adhered thereto a gas or vapor barrier layer 67 generally equivalent to the vapor barrier layer 55. The body portion 62 has first or inner recess 68. The adjacent recesses 68 form grooves opening toward the inner face 63. Similar recesses 69 are formed adjacent the outer face 65 and form outwardly opening grooves which face the vapor barrier layer 67.
In the insulation 40 as depicted in Figure 2, the slots 51 provide stress relief when the inner face 41 is cooled to cryogenic temperature. The reinforcing scrim 53 provides an effective means of terminating any cracks which might result from shrinkage of the adjacent face 41 of log portion 46 and minimize the tendency of cracks to form which would run vertically, that is in the plane of the paper. The scrim 54 adjacent the vapor barrier layer 55 provides added mechanical reinforcement to resist thermal stress on cooling of the inner face 41 of log portion 46 to cryogenic temperatures. The outer insulating layer 44 provides additional thermal insulation and mechanical protection for the vapor barrier layer 55. Accordingly, the insulation 40 effectively provides two concentric vapor barriers which provide a high degree of reliability both from a containment point of view in the event of any leakage of the liquefied gas from the tank and from any water vapor permeation from the space external to the tank. The grooves in the insulation formed by the recesses 57, 58, 68 and 69 provide convenient paths for the flow of purge gas when desired.
The thermoplastic foam used in the practice of the present invention may be any one of a variety of foams. However, particularly desirable are styrene polymer foams such as polystyrene foam having a density generally in the range of from 24 to 40 kg/m^l (1.5 to 2.5 Ib/ft³), and advantageously for many cryogenic applications, it is desirable to flexibilize the foam. This is done by a controlled crushing of the foam to render it more easily bendable. Flexibilizing of such foams is well known and set forth in U.S. Patent Nos. 3,159,700 and 3,191,224. Flexibilizing the foam employed for insulation in accordance with the present invention generally facilitates handling of the foam as it is fed to the foam depositing head. Flexibilization also increases the elongation at break of the foam and therefore reduces the tendency of such foam to crack when subjected to cryogenic temperatures.
In Figure 3, there is schematically depicted a cross sectional view of insulation in accordance with the present invention, generally designated by the reference numeral 70. The insulation 70 comprises a first insulating layer 71 and a second insulating layer 72. The insulating layer 71 is disposed adjacent the vessel to be insulated and is of the same construction as the insulating layer 43 of Figure 2. The layer 71 has an inner or cold side 73 and an outer or warm side 74. The second layer 72 is of similar construction to the layer 71 with the exception that an optional scrim beneath the vapor barrier layer 75 of the outer layer 72 has been omitted and the vapor barrier layer is directly adhered by means of a suitable hot melt adhesive 76 to the foam body portion forming the turns which make up the layer 72. The arrangement, as depicted in Figure 3, utilizing two layers of generally equal thickness provides a mechanically desirable insulation and minimizes equipment changes in the preparation of the laminate material forming the loops of each layer. On completion of the formation of the logs or insulating strips which make up the turns of the layer 71, laminates for the second layer 72 are readily prepared by omitting the scrim adjacent the vapor barrier. Thus the materials for layer 71 and 72 may be prepared and deposited without undesirable equipment changes or adjustment.
Generally, in the preparation of insulation in accordance with the present invention, it is often desirable to stagger, that is offset, the joints between the turns forming the successive layers. Such an offset or staggering minimizes the possibility of propagation of cracks in the fused joint between adjacent turns from one layer to another.
In Figure 4, there is schematically depicted a fractional cross-sectional view of an alternate embodiment of insulation in accordance with the present invention. The insulation 80 comprises in cooperative combination a first or inner insulating layer 81, a second or intermediate insulating layer 82 and a third or outer insulating layer 83. The inner insulating layer 81 comprises a plurality of loops or turns 85 joined to each other in edge to edge relationship. Each of the turns 85 comprises a first or inner body portion 86 and a second or outer body portion 87. The body portions 86 and 87 are laminated together and have therebetween a reinforcing scrim 88 such as an open weave glass cloth. A generally similar scrim 89 is affixed to the face of inner body portion 86 remote from outer body portion 87. The inner body portion 86 is provided with stress relief slots 91 which extend part-way inwardly into the body 86 from the face having scrim 89. The body portion 87 is provided with stress relief recesses, grooves, or slots 92 which extend part-way into the body portion 87 from the scrim 88. The recesses 92 may be in the form of relatively long and narrow slots, in the form of relatively short and wide grooves, or in the form of any other cross-sectional shape, i.e., rectangular, hemispherical, ellipsical or the like, to provide the desired stress relief in the inner insulating layer 81 and to prevent cracking of the insulation due to temperature stress induced in the insulating layer in a crack barrier zone which passes through the inner body portion 86 in the region of the reinforcing scrim 88. The recesses may extend inwardly as well as outwardly from the reinforcing scrim 88 part-way into the insulation and they may be provided in the inner and outer insulating layers in the two- layered structures; illustrated in Figures 2 and 3. It will be apparent that stress relief grooves (not shown) may also be provided in the intermediate insulating layer 82 illustrated in Figure 4 such that they extend part-way into the insulating material from one or opposite sides of the reinforcing scrim 107. Grooves corresponding to groove 91 may also be provided in the outer insulating layer 83 to extent part-way into the insulation from the inner side of the layer, i.e., from the side of the scrim layer 117. Each of the turns 85 has affixed thereto a reinforcing scrim 93 which is disposed on body portion 87 generally parallel to the scrims 88 and 89 and remote from scrim 88. The reinforcing scrim 93 has adhered thereto and to body portion 87 a vapor or gas barrier layer 94. The barrier layer 94 is sealed to adjacent barrier layers on the turns 85 of the first insulating layer 81. The edges of adjacent turns 85 define inwardly extending grooves 96, extending inwardly from the face having scrim 89. The adjacent turns 85 also define grooves 97 which extend inwardly from the face having the vapor barrier layer 94. The intermediate layer 82 is of the same construction as the inner layer 81 and comprises a plurality of loops or turns 85a. Each of the turns 85a comprises a first or inner foam body 101 having adjacent turns 85, a reinforcing scrim 102 affixed thereto. The body 101 defines a pair of stress relief slots 103 and 104 which extend inwardly from the scrim 102. A second generally rectangular foam body 106 is laminated to body 101 and a reinforcing scrim 107 is affixed between the bodies 101 and 106. The body 106 has affixed thereto an outer reinforcing scrim 108 which is generally parallel to scrims 107 and 102 and disposed remote therefrom. Affixed to the body 106 immediately adjacent the scrim 108 is a vapor barrier 109. The vapor barrier 109 is affixed and adhered to adjacent vapor barrier 109 of the loops or turns 85a. The turns 85a define therebetween first or inner slots or grooves 110 in the region of a fused joint 111 between the adjacent turns. The groove 110 depend generally inwardly from the scrim 102. Generally, similar grooves 112 are defined between adjacent turns 85a adjacent the scrim 108 and vapor barrier 109. The third or outer layer 83 comprises a plurality of loops or turns 115 of insulating material. Each of the turns 115 comprises a foam body 116 having a generally rectangular cross-section. The turns 115 have a reinforcing scrim 117 affixed generally adjacent the intermediate insulation layer 82. A vapor barrier layer 118 is affixed remote from and parallel to the reinforcing scrim 117. The vapor barriers 118 are adhered to the body 116 by means of an adhesive layer 119. Adjacent portions of the vapor barriers 118 of the turns 115 are adhered together and folded to lie generally at parallel to the scrim 117. Adjacent turns 115 define therebetween first grooves 121 which are inwardly facing and which extend inwardly from the scrim 117. The adjacent turns 115 also define outwardly facing grooves 122 which extend inwardly toward the grooves 121 from vapor barrier 118.
Insulation in accordance with the present invention provides considerable flexibility in the choice of materials. Generally, the innermost layer of insulating material can comprise a foam having relatively high elongation and insulating value whereas as one progresses toward the outermost layer of insulation, lower elongation in the foam may be employed depending upon the requirements of the particular insulation installation. The use of multiple vapor or gas barriers is a substantial advantage in that from a practical standpoint, it is difficult to insure the integrity of a single vapor barrier. The use of multiple vapor barriers permits the use of subatmospheric pressure adjacent the tank or container being insulated and such atmospheric pressure can be maintained adjacent the vessel employing a pump of minimal capacity.
As is apparent from the foregoing specification, the present invention is susceptible of being embodied with various alterations and modifications which may differ particularly from those that have been described in the preceding specification and description. For this reason, it is to be fully understood that all of the foregoing is intended to be merely illustrative and is not to be construed or interpreted as being restrictive or otherwise limiting of the present invention, excepting as it is set forth and defined in the hereto-appended claims.

Claims

1. An improved insulated cryogenic vessel (10) comprising at least a first containment vessel (11) having an exterior curved surface (13), a first layer of a foam insulation (43) disposed adjacent the exterior surface and covering at least a substantial portion thereof; the insulation being in the form of a plurality of turns of a composite strip-like material (43), having a continuous gas barrier layer (55) affixed thereto remote from said containment vessel, adjacent turns of the first insulation being heat bonded (48) to adjacent turns of the first insulation, characterized by a second layer of foam insulation (44) being disposed over and unadhered to the first layer of foam insulation and external thereto and spaced from the continuous gas barrier layer (55) affixed to said first layer of insulation; the second layer of insulation being in the form of a plurality of turns (61) of strip-like material, adjacent turns of the second layer of iasuiation being heat bonded to adjacent turns of insulation of the second layer of insulation; the first layer of foam insulation being a laminated strip-like material, the first layer of foam insulation having affixed thereto a first reinforcing scrim (54) and which in turn has affixed thereto said gas barrier layer (55), with a second reinforcing scrim (53) located within the laminated strip-like material, the laminated strip-like material defining a plurality of longitudinally extending slots (51) opening toward the exterior surface of the containment vessel (11), the slots terminating at a location generally adjacent said second reinforcing scrim (53).

2. The insulated cryogenic vessel of claim 1, characterized in that a second vapor barrier (67) is affixed to said second insulation layer remote from said gas barrier layer (55).

3. The insulated cryogenic vessel of claim 2, characterized in that a third reinforcing scrim (49) is affixed to the first layer of insulation and is disposed adjacent the exterior curved surface of the containment vessel with the further limitation that adjacent turns of the strip-like material (43) define inwardly facing grooves (57) adjacent the exterior curved surface of the containment vessel and adjacent turns of strip-like material (43) defining outwardly facing-grooves (58) remote from the containment vessel (11).

4. The insulated cryogenic vessel of claim 1, characterized in that another plurality of longitudinally extending slots (92) extend from said second reinforcing scrim towards said gas barrier (55).

5. The insulated cryogenic vessel of claim 1, characterized in that the foam insulation of the first layer of foam insulation is a flexibilized thermoplastic foam having a density of from about 25 to 40 kg/_m ³.